# Modifier Driver Fields

This article explains **Modifier Driver fields** in Model Reef.

You will learn:

* What modifier drivers are.
* When to use them instead of variables.
* How to apply them as multipliers or growth rates.

Modifier drivers do not represent standalone economic quantities. They are adjustment series used to shape other drivers and variables.

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### What is a modifier driver

Modifier drivers typically represent:

* Growth rates.
* Percentage uplifts or discounts.
* Seasonality indices.
* Scenario specific adjustment factors.
* FX or risk multipliers used purely as scalars.

They are almost always used inside formulas rather than reported directly.
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### Key fields for modifier drivers

When editing a modifier driver you will see fields such as:

* **Name**\
  For example `Growth - Revenue`, `Uplift - Promo`, `Index - Seasonality`.
* **Type**\
  Set to Modifier driver.
* **Units**\
  Often percentages, indices or unitless multipliers.
* **Time series grid**\
  Values per period representing the adjustment factor.
* **Notes and tags**\
  To document what the modifier does and where it is used.
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### How modifier drivers are applied

In formulas, modifier drivers are used as scalars, for example:

* `Adjusted revenue = Base revenue × Modifier driver`
* `Cost = Base cost × (1 + Inflation driver)`
* `Scenario B value = Base scenario value × Scenario modifier driver`

They do not create P\&L, Balance Sheet or Cashflow entries by themselves.
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### Scenario and branch specific modifiers

You can define modifier drivers that:

* Apply to the entire model in a scenario (for example a scenario wide discount factor).
* Apply only to a subset of variables via formulas.
* Are used to simulate shocks, discounts, price changes and other sensitivities.

Because each scenario is its own model, you can maintain different modifier profiles per scenario.
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### When to use a modifier driver instead of a variable

Use a modifier driver when:

* You want to tweak existing variable logic without duplicating variables.
* You need a reusable scalar series applied in many places.
* You want to centralise scenario specific multipliers for easy tuning.

Use a variable when the series itself should appear as a line item in financial statements.
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## Related articles

* [Dropdown Field Behaviour](/syntax/how-input-fields-work/dropdown-field-behaviour.md)
* [Entering Seasonality](/syntax/how-input-fields-work/entering-seasonality.md)
* [Modifier Drivers](/help/drivers-variables-and-timing/modifier-drivers.md)
* [Build a Sensitivity Analysis Pack](/how-tos/scenarios-and-planning/build-a-sensitivity-analysis-pack.md)


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